Typically, in a compact information terminal such as a laptop personal computer (PC) or a tablet PC, an interface (I/F) connector is installed for the purpose of establishing connection with an extension unit such as a docking station that is meant for implementing the extension function. Examples of the I/F connector for the extension function include a display port, a high definition multimedia interface (HDMI: registered trademark), and an analog interface. Other examples of the I/F connector for the extension function include an RGB port (RGB stands for Red, Green, and Blue), a USB port (USB stands for Universal Serial Bus), and an audio port. Although dependent on the number of functions in an extension unit, the I/F connector for the extension function is typically of the size of about few tens of pins to few hundreds of pins. For that reason, in a compact information terminal, the I/F connector for the extension function becomes an obstacle in achieving downsizing and slimness.
In that regard, in recent years, in order to resolve the obstacle in achieving downsizing and slimness as attributed to the I/F connector for the extension function; it has been proposed to use a USB Type-C connector, which is the new USB standard, as the I/F connector for the extension function. A USB Type-C connector is a USB connector standard that is pluggable on the front side as well as the back side. Through a USB Type-C connector; USB signals, display port signals, audio port signals, and peripheral component interconnect express (PCIE) signals can be passed in a switching manner. Moreover, a USB Type-C I/F, according to the UPD standard (UPD stands for USB Power Delivery), is possible to handle up to 100 W at 5 V to 20 V.
In the case of using a USB Type-C connector as the I/F connector, a UPD controller is installed in the compact information terminal as well as in the extension unit. Then, once the compact information terminal and the extension unit are connected to each other, the UPD controllers installed therein perform communication with each other using configuration channel (CC) signals representing USB Type-C communication signals. Subsequently, an embedded controller (EC) that is installed in the compact information terminal as well as the extension unit uses an inter-integrated circuit (I2C) and reads the communication result that is recorded in the memory of the corresponding UPD controller. Then the ECs switch the switches of the display port, the USB port, the audio port, and the power supply port. As a result, the EC installed in the compact information terminal becomes able to control the transmission of signals to the extension unit and to control the delivery and the reception of power supply in the tablet PC.
Meanwhile, the power supply delivered to the compact information terminal and the extension unit not only can be used as the USB I/O power supply as in the conventional USB standard but can also be used as the power supply for running all functions of the tablet PC and the docking station. As far as the delivery of power supply is concerned, the tablet PC not only can be the supplier of electrical power to the docking station, but can also be the supply destination and can receive electrical power from the docking station. That is, in the USB Type-C standard, switching between power feeding from one device to another device connected by a USB cable and power feeding from the other device to the former device is done depending on the situation.
Meanwhile, if an AC power supply is being used in the docking station, in the case in which electrical power is supplied to the computer from the docking station but the power delivery from the AC power supply is lost, a conventional technology is available that enables delivery of the power supply in a battery to the docking station. Moreover, a conventional technology is available in which a magnetic sensor is used in determining whether or not an extension device and an electronic device are connected.
Patent Document 1: Japanese Laid-open Patent Publication No. 10-69333
Patent Document 2: Japanese Laid-open Patent Publication No. 2009-157877
However, for example, in the case in which a commercial power supply is connected to the compact information terminal and a battery is installed in the extension unit, and when the power supply is delivered from the compact information terminal to the extension unit; the following issues arise. That is, in this state, if the delivery of power supply from the commercial power supply to the compact information terminal is cut off, the delivery of power supply is switched to the delivery from the battery installed in the extension unit to the compact information terminal. However, in UPD, it is defined that, in the case of changing the supplier of electrical power, the voltage of the power supply line is to be once dropped to 0 V. For that reason, during the switching described above, the supplier of electrical power and the supply destination are switched only after the power supply to the compact information terminal is once cut off, and then the delivery of power supply to the compact information terminal is resumed. In that case, in the compact information terminal, since the power supply is once cut off, the user data being used during a task is at the risk of getting lost.
In that regard, if the USB Type-C standard is used, even in the case of implementing the conventional technology in which, when the delivery of power supply from the AC power supply is lost, the power supply from a battery is delivered to the docking station; the operation of switching the supplier of electrical power needs to be performed thereby making it difficult to continue the delivery of power supply without disruption. Moreover, even in the case of implementing the conventional technology in which a magnetic sensor is used in determining whether or not an extension device and an electronic device are connected, the switching of power supply is not taken into account thereby making it difficult to continue the delivery of power supply without interruption.